TomotherapyandHematopoieticStemCellsforTolerancetoKidneyTransplants ABSTRACT The overarching goal of this project is to develop a tolerance induction protocol for MHC disparate kidney transplantsinrhesusmacaquesandtoelucidatetheunderlyingmechanismsoftheinductionandmaintenance ofmixedchimerismandtoleranceinthismodel.TheprimaryhypothesisisthattolerancetoMHCmismatched kidneytransplantscanbesafelyandeffectivelyachievedbyestablishingamixedchimericstateusinganewly established post?transplant non?myeloablative, helical tomotherapy?based total lymphoid irradiation (TLI)? based conditioning regimen followed by donor bone marrow?CD34+ hematopoietic cell (HSC) infusions. In addition, we will elucidate mechanisms of host immunoregulatory characteristics that are associated with successfulHSCengraftmentandmaintenanceofthechimericstate.Weproposetotestourhypothesesbymeans of 2 specific aims: 1.) Combined Bone Marrow Hematopoietic Cell/Kidney Transplants todetermine the proportionofrhesusmacaquerecipientsofdisparateunrelateddonorkidneytransplantsthatachievechimerism (without GVHD) and can be withdrawn from all immunosuppressive drugs for greater than 2 years while maintainingnormalallograftfunctionandwithoutrejection.Wewillmeasurethestateofmixedchimerismin recipientsasafunctionoftimepost?transplantandaccordingtovariousperipheralbloodandbonemarrowcell types using DNA (STR) analysis, and with flow cytometry using rhesus antibodies specific for MHC class I Mamuallelesofthedonor.2)ImmuneMonitoring,ImmunopathologyandImmunocompetence.Wewill:a.) determine early recipient immunoregulatory changes of host myeloid cells induced by the TLI?based conditioningregimenthatcorrelatewiththesuccessofbonemarrowengraftment,b.)determineifthemixed chimeric state induces changes of host dendritic cell acquisition of donor MHC class I antigen and PD?LI expression at serial time points during and after withdrawing immunosuppression, c.) characterize the developmentofrenalallograftimmuneandnon?immuneinjurybyanalysisofserialrenalallograftbiopsies,and d.)determinethedegreeofrecipientimmune?competencyafterimmunosuppressivedrugwithdrawalbytesting the recall T cell responses to cytomegalovirus antigens and tetanus toxoid. Knowledge gained through this rhesus tolerance induction protocol, including the underlying immunological mechanisms, will have direct relevance to a variety of deceased donor transplants. Furthermore, it will set a new course of healthcare innovationanddeliverythatwillgreatlybenefittransplantpatients,andotherpatientpopulations.